Biodegradable polymers are becoming widely used in various fields of biotechnology and bioengineering, as implants for tissue engineering, surgical devices and for drug delivery. For example, regular AA-BB-type bio-analogous poly(ester amides) (PEAs), poly(ester urethanes) (PEURs), and poly(ester ureas) (PEUs), which consist of nontoxic building blocks, such as hydrophobic α-amino acids, aliphatic diols and di-carboxylic acids. These bio-analogous polymers have been proven to be important materials for biomedical applications because of their excellent blood and tissue compatibility (K. DeFife et al. Transcatheter Cardiovascular Therapeutics—TCT2004 Conference. Poster presentation. Washington D.C. 2004; J. Da, Poster presentation, ACS Fall National Meeting, San Francisco, 2006) and biologic degradation profiles (G. Tsitlanadze, et al. J. Biomater. Sci. Polymer Edn. (2004). 15:1-24). Controlled enzymatic degradation and low nonspecific degradation rates of PEAs make them attractive for drug delivery applications.
Because many biomedical devices are implanted in a bodily environment that undergoes dynamic stress, the implants must be sufficiently elastic to undergo and recover from deformation without subjecting the host's surrounding tissue to irritation and without mechanical breakdown of the polymer. Ideally such implants would have properties resembling those of the extracellular matrix, a soft, tough and elastomeric proteinaceous network that provides mechanical stability and structural integrity to tissues and organs. Such a polymer network would allow ready recovery from substantial deformations.
Various classes of biodegradable polymer elastomers have been disclosed: Elastin-like peptide elastomers are based on protein polymers and are produced recombinantly. Polyhydroxyalkanoates, such as poly-4-hydroxybutyrate, have also been used as elastomeric polymers. Hydrogels have been proposed based on such various compounds as alginate, vegetal proteins crosslinked with synthetic water soluble polymer (PEG), and cross-linked hyularonic acid. Recently a covalently cross-linked and hydrogen bonded three-dimensional polymer network in which at least one monomer is trifunctional has been described for use in polymer implants (Y Wang et al., Nat. Biotech (2002) 20:602-606).
Heretofore interpenetrating networks have found many applications as automotive parts (tires, belts, and bumpers), hoses, cables, gaskets, damping compounds, ion-exchange resins, optical fibers, medical gear, artificial teeth, and dental fillings, In addition, U.S. Pat. No. 5,837,752 describes a polymer composition that forms a semi-interpenetrating network made from a linear biodegradable hydrophobic or nonbiodegradable hydrophilic polymer and cross-linkers that include a degradable linkage, such as an anhydride linkage.
Despite such progress in the art, there is need for new and better polymer blends, such as those that can form non-biodegradable or biodegradable interpenetrating networks. In particular there is a need for polymer compositions suitable for forming elastomeric implantable devices of various types, including those used in tissue, tooth, and bone replacement.